ABSTRACT

Over the past couple of decades, a rapid penetration of distributed generators (DGs) such as photovoltaic (PV), energy storage systems (ESSes), wind turbines and others has occurred in electrical power system. DG units can potentially significantly reduce pollution and decrease the power transmission losses, while improving the power availability and reliability at the same time. However, since the legacy grid has not been initially designed to accept such DGs, a solution to simplify the integration of DG units to the main grid through a so-called microgrid (MG) entity was proposed. MG could consist of several parallel-connected DGs, where each one of them is interfaced through a controllable power electronics interface. The significant challenge to be overcome in MG technology is to realize the operation of paralleled connected power electronics converters with good load sharing ability in both steady state and transient conditions. The conventional principle of controlling these converters is based on droop control loops. However, such a structure has inherent limitations. Firstly, it has very poor transient characteristics, because powers are calculated based on low pass filters while the accuracy of active and reactive power control of a given converter heavily depends on the nature (R/L ratio) of the lines between the converters and the buses to which they are connected. Moreover, as the converters normally have an LC filter installed at the output, there exist a dynamic coupling between the inductor current and capacitor voltage, which is cumbersome to explicitly cancel due to presence of computational, and pulse width modulation (PWM) delays. This project aims to develop a new control strategy for paralleled converters which will be much more suitable for integration of pulsed power loads due to inherently fast characteristics. Both theoretical research and experimental demonstration will be developed to study various aspects of the problem.